What is Pegasus' weaknesses?

Pegasus is not portrayed with a weakness. The closest thing for him is the touch of an immortal being; the mortal Bellerophon, who is famous for being the only human to have tamed Pegasus, could not ride the horse if he didn't have the golden bridle of Athena or Hera. Others say that he consented to let Bellerophon ride him only because Athena asked to him, and most people don't refuse a god/goddess.